Method and system for improve-efficiency air-conditioning

ABSTRACT

Systems and methods for circulating air in an enclosed environment are disclosed. In some embodiments, the system includes an inlet to receive air from outside of the enclosed environment and an air handling unit coupled to the inlet and also configured to receive circulated air from the enclosed environment. The air handling unit can be configured to affect a temperature of at least one of the received outside air and the received circulated air. Based on the received outside air and the received circulated air, the air handling unit can be further configured to generate air for supplying to the enclosed environment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/937,320, filed on Jul. 9, 2013, which is a continuation of U.S.patent application Ser. No. 13/440,356, filed on Apr. 5, 2012, (now U.S.Pat. No. 8,491,710), which is a continuation of U.S. patent applicationSer. No. 13/109,833, filed on May 17, 2011, (now U.S. Pat. No.8,157,892), which claims priority to and is a continuation-in-part ofU.S. patent application Ser. No. 12/848,788 to Meirav, filed Aug. 2,2010, and entitled “Method and System for Improved-EfficiencyAir-Conditioning,” which claims priority to U.S. Provisional PatentApplication No. 61/345,194, filed May 17, 2010, and U.S. ProvisionalPatent Application No. 61/351,968, filed Jun. 7, 2010. The disclosuresof the above applications are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present application generally relates to air circulation systems andin particular to removal of various substances from and/or cleaning ofair circulation systems.

BACKGROUND

Heating, Ventilation and Air-Conditioning (“HVAC”) are standard invirtually every modern building. Indeed, HVAC is often one of thelargest parts of the entire energy budget of most buildings. This isparticularly the case in extreme climates, both hot and cold. One of thegoals of HVAC systems is to provide comfortable and healthy environmentfor building occupants, in terms of temperature, humidity, compositionand cleanliness of air.

Central HVAC systems in buildings typically include one or more centralair handling unit(s) and an air distribution system, where supply air isdirected to various parts of a building through a network of ducts, andreturn air flows from these spaces, through other ducts or a plenum,back to the air handling unit(s). In the air handling unit, the air iscooled and/or heated, as well as filtered and often dehumidified and/orhumidified, as needed. Thus, HVAC systems constantly circulate airthrough the building while continually adjusting its temperature andhumidity to maintain comfortable environment.

However, in order to maintain good air quality, not all the air isrecirculated. Some of the air leaks out through doors, windows, etc. andsome fraction of the circulating air is intentionally exhausted outsidethe building. This is referred to as exhaust air. The exhaust air isreplaced by an intake of outside air, also known as makeup air, to makeup for the exhaust air being taken out. This is also referred to as“fresh air” or ventilation. This replacement of air is done becauseoccupants of the building and the equipment consume oxygen and emitcarbon dioxide (CO₂) as well as a variety of other contaminants thatgradually compromise quality and safety of the air. Such replacement ofthe air maintains fresh air quality.

Oxygen represents approximately 21% of atmospheric air and that isnormally the desired level of indoor air as well. On the other hand CO₂is present only in very low levels in the outside air, typically at alevel of approximately 400 parts per million (“ppm”). Once elevatedlevels of CO₂ or reduced levels of oxygen are created, a fairlysignificant amount of outside air is needed to bring their respectiveconcentrations close to the desired level. Indeed, to fully restoreoxygen and CO₂ concentration virtually all the air may need to bereplaced.

The outside air represents an additional, and depending on the outsideclimate conditions often a significant, thermal load on the air handlingunit. In the case of a hot and humid climate, for example, the outsideair injected into the HVAC system can require additional energy forcooling and dehumidifying the outside air and can represent asignificant fraction of the entire thermal load and energy usage of theHVAC system.

The amount of exhaust air and outside air can be adjusted to meet theair quality standards. Certain minimum amounts of levels of oxygen, CO₂and other contaminants, a variety of organic gases collectively referredto as volatile organic compounds or VOCs, are often set to maintain airquality. In the USA, the American Society of Heating, Refrigeration andAir-conditioning Engineers (“ASHRAE”) issues guidelines, including theASHRAE Standard 62, for the amount of outside air ventilationrecommended for a given space and number of occupants. However, thegreater the rate of air replacement, the more energy is consumed by theHVAC system.

SUMMARY

In some embodiments, the amount of supply air used by an HVAC system,and hence the amount of energy used for heating and cooling, whilemaintaining desirable air quality and composition, can be reduced byremoving unwanted substances such as gases, including carbon dioxide(CO₂), contaminants, particles, etc. using scrubbers or other devicesthat can separate these gases from the circulating air. Optionally, thequality of air can be further improved with injection of concentratedoxygen. In some embodiments, a fraction of the circulating air can bediverted though the scrubbers to achieve the desired result. While in anormal HVAC system frequent extensive replacement of the building air isperformed, scrubbing of CO₂ and other unwanted gases and vapors, canachieve the same goal, but with much lower thermal load on the HVACsystem, thereby providing significant energy saving for the building andreducing demands on the entire electrical grid.

In some embodiments, the HVAC system can include an oxygen injectionsystem that can inject oxygen-enriched air into the circulated air.

In some embodiments, a control system for use with an HVAC system caninclude a gas scrubbing system for removal of an unwanted substance gasfrom circulated air. The control system can include a sensor fordetermining an amount of the unwanted substance(s), particle(s),gas(es), etc. in the circulated air. A minimum level of outside airreplacement can be maintained, and a controller can modify a rate ofexhaust of circulating air and intake of outside air so as to adjustoverall air replacement according to the measured amount of unwantedsubstance(s), particle(s), gas(es), etc. in the circulated air. Thecontrol system also can include an oxygen sensor for determining anamount of oxygen in circulated air. The controller can further modifythe rate of oxygen injection.

In some embodiments, the system can be a modular system that can beconnected to an HVAC system that can circulate air in an enclosedenvironment. The modular system can include a module for scrubbingconfigured to reduce a level of an unwanted substance in the circulatingair.

In some embodiments, the current subject matter relates to a system forcirculating air in an enclosed environment. The system can include aninlet configured to receive an outside air from outside of the enclosedenvironment and an air handling unit coupled to the inlet to receive theoutside air through the inlet and configured to receive a circulated airfrom the enclosed environment. The air handling unit can be configuredto affect a temperature of at least one of the received outside air andthe received circulated air. Based on the received outside air and thereceived circulated air, the air handling unit can be further configuredto generate air for supplying to the enclosed environment. The currentsubject matter system can also include an air circulation systemconfigured to circulate the generated air from the air handling unit tothe enclosed environment and back to the air handling unit and ascrubbing system coupled to at least one of the air handling unit andthe air circulation system and configured to reduce presence of at leastone substance in the air supplied to the enclosed environment.

In some embodiments, the current subject matter relates to a process forcirculating air in an enclosed environment. An outside air from outsideof the enclosed environment and a circulated air from the enclosedenvironment are received. At least one of the received outside air andthe received circulated air are conditioned so as to supply at least oneof the received outside air and the received circulated air at a desiredtemperature to the enclosed environment. The conditioned air iscirculated into and from the enclosed environment. At least some of thereceived circulated air from the enclosed environment is scrubbed toreduce presence of at least one substance in the circulated air. Thescrubbed air is recirculated. At least a portion of the circulated airis exhausted from the enclosed environment.

In some embodiments, the current subject matter relates to a controlsystem for use with an HVAC system having a gas scrubbing system forremoval of an unwanted gas from circulated air. The control system caninclude a sensor for determining an amount of the unwanted gas in thecirculated air and a controller configured to modify a rate of exhaustof circulated air or intake of outside air so as to adjust an overallair replacement according to the measured amount of unwanted gas in thecirculated air.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The current subject matter is described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, whereapplicable, the left-most digit(s) of a reference number identifies thedrawing in which the reference number first appears. In the figures:

FIG. 1 is a block diagram illustrating an HVAC system;

FIG. 2A is a block diagram illustrating an exemplary HVAC systemincorporating substance scrubbing and oxygen injection components,according to some embodiments of the current subject matter;

FIG. 2B is a block diagram illustrating another exemplary HVAC system,according to some embodiments of the current subject matter;

FIG. 2C is a block diagram illustrating yet another exemplary HVACsystem, according to some embodiments of the current subject matter;

FIG. 3 is a block diagram illustrating an exemplary HVAC system that caninclude a configuration of valves and lines allowing the scrubber toswitch from an adsorption mode to a purge mode, according to someembodiments of the current subject matter;

FIG. 4 is a block diagram illustrating an exemplary HVAC system that caninclude an oxygen injection system, according to some embodiments of thecurrent subject matter;

FIG. 5 illustrates an exemplary control flow for a controller for anHVAC system, according to some embodiments of the current subjectmatter; and

FIG. 6 is a flow chart illustrating an exemplary method according tosome embodiments of the current subject matter.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating a circulating central HVAC system100. The system 100 can be configured to provide air circulation to anoccupied space 102 to which it is connected. The system 100 furtherincludes an air handling unit (“AHU”) 106, which has both heating andcooling elements that modify temperature of the circulating air as itflows and comes in contact with these elements. The system 100 canfurther include air intake duct(s) 108 connected to the AHU 106 viacirculation lines 104 that allow intake of outside air (“OA”) into thesystem 100 and specifically AHU 106. The system 100 can also includeexhaust duct(s) 112 that receive return air (“RA”) via lines 110 andexpunge it as an exhaust air (“EA”) into the outside atmosphere (or anyother environment).

In operation, the fans or blowers that can be disposed in the AHU 106force the flow of the conditioned supply air (“SA”) through ducts thatdistribute the conditioned air throughout the various parts of theoccupied space 102 (which can be an enclosed environment). For ease ofillustration, the following description refers to a building as anexample of an enclosed environment 102. The building 102 can havedifferent zones for which rates of air flow can be different. Return aircan flow back to the air handling unit 106 via lines 114 and can befiltered to remove particles, bacteria, substances, various fumes,and/or a combination thereof. Some of the return air can be exhaustedoutside the building 102 as exhaust air. The air can be exhaustedthrough valves that control the amount of exhaust air being released. Atthe same time, fresh outside air can be pulled in to replace the exhaustair and maintain a correct overall volume and pressure of air in thebuilding 102. Typically 10-15% of airflow can be released as exhaust andreplaced, but this number can vary widely. In some environments, such asbathrooms and kitchens, the HVAC system can be configured to exhaust andreplace 100% of the air flow. The constant replacement of exhaust airwith outside air can be intended to maintain good air quality, and inparticular, replenish oxygen consumed by the building occupants andremove substances, particles, gases (e.g., carbon dioxide), fumes othercompounds, and/or a combination thereof generated by occupants,equipment and/or materials located inside the enclosed environment 102.

In some embodiments, the enclosed environment 102 can be an officebuilding, a commercial building, a bank, a residential building, ahouse, a school, a factory, a hospital, a store, a mall, an indoorentertainment venue, a storage facility, a laboratory, a vehicle, anaircraft, a ship, a bus, a theatre, a partially and/or fully enclosedarena, an education facility, a library and/or other partially and/orfully enclosed structure and/or facility which can be at times occupiedby equipment, materials, live occupants (e.g., humans, animals,synthetic organisms, etc.), etc., and/or any combination thereof.

FIGS. 2A, 2B and 2C are block diagrams schematically illustratingvarious ways to incorporate air scrubbers in the HVAC system 100 shownin FIG. 1 to allow reduction of exhaust air and outside air. FIG. 2Aillustrates an HVAC system 202 that can be configured to incorporate ascrubber (“CS”) 204 in line 114 that connects the intake line 104 andthereby the AHU 106 and the return air line 110. The return airtravelling along the line 110 can be split into a fraction that isdiverted to the CS 204 and another fraction diverted to the exhaust duct112 for expunging into the atmosphere.

FIG. 2B illustrates another exemplary way of incorporating a scrubberinto an HVAC system. As shown in FIG. 2B, an HVAC system 206 can includea scrubber 208 that is connected to the line 114 (as opposed to beingplaced in the line 114, as shown in FIG. 2A). The return air travellingalong the line 110 can be split into two fractions: one going to theexhaust duct 112 and the other going to the line 114. The fraction ofthe return air that travels along the line 114 can be further split intoa fraction that bypasses the CS 208 and the one that travels into the CS208 for scrubbing. Once the CS 208 scrubs or “cleans” that fraction, itis re-entered into the line 114 for supplying to the AHU 106, as shownby the arrows in FIG. 2B.

FIG. 2C illustrates yet another exemplary way of incorporating ascrubber into an HVAC system. In this case, system 210 can include ascrubber 212 in the line 104 placed between the AHU 106 and the occupiedspace 106. Hence, any air that is travelling through the AHU 106 can bescrubbed or “cleaned” by CS 212 immediately before it enters theoccupied space 102. Other ways of incorporating a scrubber into an HVACsystem are possible.

In some embodiments, only a fraction of the circulating air stream canbe diverted to the scrubber, which can intercept the flow of thediverted air. The scrubber can subsequently allow scrubbed air tocontinue to flow back into the general circulation with substances,compounds, particles, fumes, gases (e.g., CO₂), etc. partially and/orfully captured, filtered, and/or removed from the scrubbed air. As shownin FIGS. 2A-C, the scrubber can be implemented in many different ways.

In some embodiments, to absorb substances, compounds, particles, fumes,gases, etc. the scrubber 204, 208, 212 can use adsorbent materials,molecular sieves, porous materials, sponge-like materials, electricallyand/or electro-magnetically charged liners or objects, any otherchemical, biological attractants, and/or any combination thereof. Suchmaterials can be placed in a container, stacked in columns, disposed asa sheet or a lining the inside of one or more lines of the system shownin the FIGS. 1-5. For example, several porous materials have been shownto be effective adsorbents of CO₂, notably a number of syntheticzeolites, but also porous alumina, and metal organic frameworks. Theseare readily available from a variety of commercial sources, such as W.R.Grace SYLOBEAD® C-Grade 13X, Intera Global Corporation's mSorb®, andgeneric producers such as Pingxiang XINTAO Chemical Packing Co., Ltd. InChina, GHCL Ltd., in India, and many others. Zeolite beds have beendeveloped to extract CO₂ from a gas stream for various industrialapplications (e.g., U.S. Pat. No. 3,619,130 to Ventriglio et al.; U.S.Pat. No. 3,808,773 to Reyhing et al.; U.S. Pat. No. 3,751,848 toCollins; U.S. Pat. No. 3,885,928 to Shermen et al.; U.S. Pat. No.4,249,915 to Sirkar et al.; U.S. Pat. No. 5,137,548 to Grenier et al.).For the purposes of adsorption of CO₂ such technologies can be adoptedfor use by the current subject matter HVAC systems and can be moreforgiving in terms of the allowed residual CO₂ in the outflow. In someembodiments, addition of other adsorbents, including multiple zeolites,porous alumina (e.g., U.S. Pat. No. 4,433,981 to Slaugh et al.; U.S.Pat. No. 4,711,645 to Kumar et al.) or activated charcoal (e.g., U.S.Pat. No. 1,522,480 to Allen; U.S. Pat. No. 1,836,301 to Bechthold) canimprove air quality or energy efficiency by removing other gases,volatile organic compounds and humidity or by allowing lower-temperaturerelease of adsorbents.

More recent developments in the field of solid adsorption or CO₂ includemetal organic frameworks (U.S. Pat. No. 6,930,193 to Yaghi et al.; U.S.Pat. No. 7,662,746 to Yaghi et al.) and amine-impregnated clays (U.S.Pat. No. 6,908,497 to Siriwardane). These adsorbents can be suitable foruse in the current subject matter systems described herein. The currentsubject matter system can be implemented with any past,currently-available, and future adsorbents designed to scrub or “clean”air. In some embodiments, the combination of several differentadsorbents in the same unit or as separate units may offer the betterperformance.

FIG. 3 illustrates an exemplary scrubber system 300 that can beincorporated into systems shown in FIGS. 1 and 2A-C, according to someembodiments of the current subject matter. The system 300 includes ascrubber 310, a circulating supply air valve 302 (“Valve 1”), aback-to-circulation valve 304 (“Valve 2”), a purge inlet valve 308(“Valve 3”), and a purge exhaust valve 306 (“Valve 4”). The scrubber 310can be configured to operate in two cycles: an adsorption cycle and aregeneration cycle, as discussed below. During the adsorption cycle,Valves 1 and 2 are open and can allow entry of, adsorption ofsubstances, particles, fumes, gases, etc. from, and subsequent exit ofthe circulating air. During this cycle, Valves 3 and 4 are closed.Whereas, during the regeneration cycle, Valves 1 and 2 are closed, whileValves 3 and 4 are open. Valves 1 and 2 can couple the scrubber 310 tothe circulating lines, whereas Valves 3 and 4 can couple the scrubber310 to the purging lines, as shown in FIG. 3.

As such substances, particles, fumes, gases, hazardous vapors (e.g.,radioactive vapors) etc. (hereinafter, “substances”) captured from thecirculating air accumulate in the scrubber 310, the substances can beremoved from the scrubber 310 at a predetermined rate. Removal ofsubstances can be referred to as a “regeneration” or a “regenerationcycle”. Such substances can be released into the atmosphere or otherwisecollected, disposed of, sequestered, and/or any combination thereof.Regeneration can be achieved by a combination of heating, purging,pressure change, electrical energy, and/or any combination thereof. Insome embodiments, the release of substances can be achieved by acombination of heating and purging with air or other purge gas. Thus, anadsorption-desorption cycle can sometimes be referred to as atemperature-swing adsorption.

As stated above, during the regeneration cycle, the scrubber 310 can beisolated from the HVAC system circulation by Valves 1 and 2, shown inFIG. 3, and instead, can be connected to the incoming and outgoingpurging lines using Valves 3 and 4. While Valves 1 and 2 are closed andValves 3 and 4 are open during the regeneration cycle, purge gas, air,and/or any other purge substance can be configured to flow through thescrubber 310 while it is isolated from the air circulation system. Thescrubber 310 can run the adsorption and regeneration cycles atperiodically, at predetermined times, and/or as necessary (for example,upon detection of adsorption of a particular substance or a specificamount of a substance). The scrubber 310 can be also configured to runeach cycle for a predetermined period of time. Alternatively, the lengthof time that each cycle can be performed depends on the substanceadsorbed/purged, time that it takes to adsorb/purge a substance or aparticular amount of the substance, interior conditions, exteriorconditions, type of the occupied space 102, energy usage, environmentalregulations, commercial factors, and/or any other factors, and/or acombination of factors. If the scrubber regeneration interrupts thecontinual scrubbing process for an unacceptably long period of time,multiple scrubbers (not shown in FIG. 3) can be used to avoid suchinterruption, so that when one scrubber is undergoing regeneration,another scrubber can be engaged in one of the cycles. Shortinterruptions in operation of the scrubber will likely not pose aproblem with air circulation, as long as the aggregate amount ofsubstances, CO₂, VOCs, etc. removed over extended periods of severalhours is sufficient. Similar multiple-system back up can be implementedfor other components of the system, such as an oxygen concentrator(s).

In some embodiments, the scrubber adsorbent bed design can include anappropriate choice of adsorbent material, its amount, its spatialdistribution, an air flow pattern and its overall capacity can becompatible with various airflow design requirements. In designing thescrubber, system size and cost versus throughput, frequency ofregeneration and energy requirements for regeneration can be alsoconsidered. The amount of substances, CO₂, VOCs, etc. that can becollected and released in each temperature swing adsorption cycle candepend on the amount of active and accessible adsorbent material, andfor certain adsorbents can depend on the temperature gap between theadsorption and purge cycle. Thus, to achieve a certain rate of gascapture one can use less material and operate with more frequent purgecycles. The cycles as well as their frequency can also depend on naturalkinetic rates of adsorption and desorption for a particular material,flow rate and temperature that constrain the cycle time for a givenamount of material. To minimize energy required, i.e., the energy thatcan be required to heat the purge gas, a lower purge gas temperature canbe used, which can reduce the amount of material desorbed per cycle. Inan application that is primarily driven by energy savings, one can startwith the temperature and volume of purge gas that can be generated usingan excess heat of the HVAC system and use that available purgetemperature to design the thermal range of the temperature swing cycle,which in turn will determine the kinetics of the adsorbent design thedimensions of the bed.

In some embodiments, an HVAC system having temperature swing adsorptionwith solid adsorbents can provide simplicity, durability, scalability todifferent sizes, and a relatively low operating cost. There are manyother ways to remove substances, CO₂, VOCs, as well as other unwantedgases, fumes, and/or vapors. In some embodiments, substance, CO₂, VOC,etc. scrubbing can be achieved by reactions with alkaline hydroxidebases. In some embodiments, substance, CO₂, VOC, tec. scrubbing can beachieved using aqueous amine gas solutions, such as monoethanolamine orother amines that are well known. In some embodiments, scrubbing can beachieved by a chemical cycle in which sodium carbonate combines withcarbon dioxide and water to form sodium bicarbonate (e.g., U.S. Pat. No.3,511,595 to Fuchs). Other techniques for removal of substances, CO₂,VOCs, etc. can include selective membranes, for example, PRISM membranesfrom Air Products, Inc, or CYNARA membranes from Cameron InternationalCorp. Since the scrubber can be a separate module in this systems, otherscrubbing technologies (past, currently available, or future) can beused in such system without having to change its other components.

In some embodiments, to regenerate the scrubber, at least some of theabove techniques can use heat for regeneration. Some of that heat can beobtained by harvesting waste heat produced by other systems nearby,including the compressor and the air handling unit of the HVAC system,as well as solar energy. This can further improve the overall economicsof the system. In some embodiments, the purging of the adsorbent bedutilizes warm air from the cooling unit to purge the bed duringregeneration. In some embodiments, solar energy can be collected on arooftop unit and/or a separately located unit and used to heat the purgegas. Solar heating and harvesting compressor heat and other wasted heatcan be used in combination with one another to minimize the energy usageof the system as a whole. Independent or additional heating can beperformed to achieve a particular purge gas temperature in which case aheating coil, a furnace or a gas burner can be incorporated to thesystem before the entry point of the purge gas.

Referring back to FIG. 2A, the scrubber (CS) 204 can be configured tointercept all of the return air flow, which might not be necessary orpractical. This is illustrated in FIG. 2B, where only some of the returnair can be diverted to the scrubber 208 while the rest of the air canbypass the scrubber 208 and can flow directly to the air handling unit106. In some embodiments, it is not essential that all of the air passthrough the scrubber, as long over time a sufficient fraction of theunwanted substances, gases, etc. are captured and removed from thecirculating air stream. In an embodiment shown in FIG. 2C, the scrubber212 can be positioned downstream from the air handling unit 106, whichhas the advantage of colder air entering the scrubber and cooling it.Many scrubbing technologies and adsorbents can perform better with lowertemperatures. From an air quality standpoint, any location of thescrubber can work, as long as there is over time adequate amount ofcontact between the circulating air and the scrubber somewhere along theflow path of the air before or after the air handling unit. In someembodiments, the scrubber(s) can be distributed in the occupied space102.

In some embodiments, the scrubber can collect CO₂ and potentially othersubstances that can be disposed of in various ways. The collectedsubstances can be released to the atmosphere, collected in containersfor handling and disposing at another location, flowed through pipelinesto another location or facility to be stored, processed and/or utilized,or otherwise disposed of in any other fashion. For example, CO₂ isbeneficial for greenhouses and could be directed to such greenhouses bypipes or by containers. Alternatively, these byproduct gases can besequestered indefinitely simply to avoid releasing them into theatmosphere. There can be a higher cost to such disposition of thesegases and, in some situations, it might not necessarily be economicallyjustifiable to do so.

FIG. 4 is a block diagram illustrating an HVAC system 400, according tosome embodiments of the current subject matter. The system 400 includesan air handling unit 402 configured to supply air circulation to anoccupied space 102 via line 104, where return air is transported vialine 110. The system 400 also includes a scrubber 404 that is disposedin the line 114 connecting the supply air line 104 and the return air110. The scrubber 404 can be disposed in any other fashion (asillustrated in FIGS. 2A-2C) and can be configured to perform airscrubbing discussed above. The system 400 further includes an oxygenconcentrator 406. The oxygen concentrator 406 can take its own outsideair supply (“OA2”), as shown by the arrows, and can create a flow ofconcentrated oxygen (“O”) into the supply air line 104. The concentratedoxygen can be directed through an additional intake valve in to the airhandling unit 402, upstream from the heating/cooling elements. Theoxygen concentrator 406 can dispose of nitrogen (“N”), as indicated bythe arrow in FIG. 4, and potentially other by-products back to theatmosphere (or any other location, container, etc.). The amount ofoxygen added to the circulating air can depend on flow rate and theoxygen concentration. In some embodiments, the latter can besubstantially greater than 90% (e.g., as is the case in mostcommercially available concentrators). However, a lower concentrationcan be also used to achieve the desired results with a slightly higherflow rate.

The oxygen concentrator 406 can be implemented in a number of ways. Insome embodiments, the technique for oxygen concentration can include aknown Pressure Swing Adsorption (“PSA”) technique, Vacuum SwingAdsorption (“VSA”) technique, and/or any other technique and/or anycombination thereof. Systems employing these techniques can come indifferent sizes and output capacities, as stand-alone systems forproviding concentrated oxygen directly from air, as well as in any otherforms. Example VSA oxygen generating systems include at least one of thefollowing: the PRISM VSA oxygen generation systems by Air Products Inc.;the OXYSWING product line by Innovative Gas Systems, Inc.; the ADSOSSline of oxygen generators by Linde; the VPSA oxygen generating systemfrom Praxair Inc. These PSA/VSA systems can utilize highly porousadsorptive solids, usually a synthetic zeolite bed, in one or morecontainer, typically shaped as a cylindrical column, and can use pumpsand compressors to change the pressure of gases in these containers. Thetechnique can rely on differential adsorption of oxygen and nitrogenonto the adsorbent. Thus, it can take an inflow of normal air (or othergas mixtures) and generate two separate outputs: an oxygen-concentratedair and oxygen-depleted air. One of the advantages of PSA/VSA systems isthat these systems can continually generate oxygen for extended periodswithout much maintenance.

Other ways to separate or concentrate oxygen are also available.Cryogenic separation can be an effective way for large volumes and highpurity, where the different condensation/boiling temperatures ofdifferent gases are used to separate oxygen from air. Selectivemembranes and selective diffusion media can also separate oxygen fromair. Concentrated oxygen can also be generated from electrolysis ofwater, where electrical current through water generates oxygen gas onone electrode and hydrogen gas at the other. While these are energyintensive processes, pure hydrogen or nitrogen created as by productsand can be collected and utilized for other applications.

In some embodiments, the presence of both the scrubber 402 and theoxygen concentrator 406 does not eliminate exhaust air and outside air.In some embodiments, exhaust air and outside air can be kept at acontrolled level, which can be lower than in a conventional HVAC systembut at a level that can be warranted or desired in order to assure thatthere is no gradual deterioration in air quality despite the benefits ofthe oxygen concentrator and the scrubbers.

In embodiments where the oxygen concentrator 406 is not used, thescrubber 404 can be configured to provide a majority of benefits relatedto circulation of quality air. This can be useful in scrubbing of carbondioxide. While oxygen consumption and CO₂ emission go hand in hand andoccur in almost identical molecular quantities, which can imply that adrop in oxygen concentration can be commensurate with a rise in CO₂levels, as long as makeup air in the HVAC system is not eliminatedaltogether, even without a scrubber and an oxygen source, the oxygen andCO₂ levels can stabilize at certain asymptotical concentrations thattogether sum up approximately to 21%, the same as that of outside air.The asymptotic level of oxygen, X, is given by

X=X ₀ −B _(o) /M  (1)

where X₀ is the concentration of oxygen in outside-air, B_(o) is the netamount of oxygen consumed (in CFM, liters/second or any other units) bythe occupants and M is the amount of outside air injected (in sameunits, CFM, liter/second, etc respectively). Similarly, CO₂ level, Y,can be calculated by

Y=Y ₀ +B _(c) /M  (2)

where Y₀ is the concentration of CO₂ in outside-air and B_(c) is the netamount of CO₂ produced by the occupants of the occupied space. Thus, aslong as B_(c)≈B_(o), at least approximately, then X+Y≈X₀+Y₀. However,adding a scrubber that extracts CO₂ at a rate, S_(c), (in same units,CFM, liter/second, etc. respectively) can result in

Y=Y ₀+(B _(c) −S _(c))/M  (3)

Analogously, the impact of an oxygen generator injecting at a net rateof G_(o) (in same units, CFM, liter/second, etc., respectively) canchange the asymptotic value of X to

X=X ₀−(B _(o) −G _(o))/M  (4)

Example

For illustration purposes only, to understand why oxygen replenishmentis less critical, the following example is provided: if outside air isat the normal 21% oxygen, and occupants of the occupied space consumeoxygen at a rate of 2 CFM (cubic feet per minute) and exhale CO₂ at asimilar rate, and if makeup air is at a relatively low 100 CFM, with noscrubbing or oxygen injection, then oxygen can gradually approach 19%,while CO₂ can approach 2%. There can also be elevated levels of otherVOCs alongside the CO₂. Whereas a 19% concentration of oxygen can beacceptable, a 2% concentration of CO₂ is not. Further, the VOC levelsmost likely will be unacceptably high as well. Thus, adding a scrubberwith S_(c)=2 CFM capacity alone could bring CO₂ levels down to normal.Oxygen can still be depleted approximately to 19%, unless supplementaloxygen is injected, but even so air quality might be acceptable at thislevel even without an oxygen source, and can require less hardware andless operating costs.

FIG. 5 illustrates an exemplary HVAC system 500 that includes an airhandling unit 504, a central control system (“CC”) 502, a scrubber 506,and a plurality of sensors (“Y”) 531, 533, 535 that can be installed inthe occupied space 102. Connections of the AHU 504 and CS 506 as well asthe supply air and return air lines similar to the ones shown anddiscussed in connection with FIGS. 1-4 above. The central control system502 can be coupled to the components in the system 500 via variousconnections (e.g., electrically, wirelessly, wired, wireline, etc.) andcan be configured to control them via issuance of various commands. Thecentral control system 502 can include a processor, a memory, a monitor,and or any other components. It can control/operate componentsautomatically, manually, or semi-automatically. The central controlsystem 502 can be coupled to sensors 531, 533, 534 via connections 514,to the scrubber 506 via connections 516, and to the ducts 108, 112 viaconnections 512. The system 502 can be also configured to control AHU,an oxygen concentrator (not shown), and/or any other components.

The sensors 531, 533, 535 can be installed in various locations in theoccupied space 102 and can be configured to provide a feedback to thesystem 502 system. Sensors (Y) can be distributed through the occupiedspace and detect levels of one or more substances, gases (such as CO₂and/or oxygen, and other gases), fumes, vapors, VOCs, etc., and/or anycombination thereof. Sensors for CO₂ are commercially available,examples of which include C7232 sensor from Honeywell Corp., TELAIREsensors from General Electric, etc. Upon detection of and/or aparticular concentration such substances, gases, etc., the sensor(s) (Y)can be configured to generate a data signal that can be transmitted tothe central control system 502 for processing. After processing the datasignal(s), system 502 can generate appropriate commands to componentswithin the system 500 (e.g., turn on a regeneration cycle of thescrubber 506; perform adsorption cycle at a predetermined time or whenconcentration of a substance reaches a certain level).

As stated above central control system (CC) 502 can be human operated,automated and/or computerized and can detect a signal from the sensors(Y). Based on these and the various parameters and settings of thesystem 500, the CC 502 can control and/or modify at least one of thefollowing, in order to achieve targeted conditions: OC power (on/off),OC settings, OC valves (OC is not shown in FIG. 5), CS settings, CSregeneration trigger, outside air flow rate, exhaust air flow rate, andany other functions. The system 502 can have fail safe measures toprevent unwanted elevation of oxygen, and the ability to shut downeither or both oxygen concentrator and scrubber if needed and compensateby increasing outside air and exhaust air levels to those of aconventional HVAC.

The control system 502 can permit the amount of scrubbing or injectionof oxygen to be adjustable, whether directly or indirectly, whetherelectronically or manually. Adjustments can be achieved by changing thepower or settings applied to the various compressors, pumps, motors,heaters, actuators or valves associated with the scrubbers and theoxygen concentrators. The adjustments to the amount of scrubbing oroxygen injection can be automatically done in response to a measurementof air quality or air composition in one or more locations. Theadjustments to the amount of scrubbing or oxygen injection can also beautomatically done based on building occupancy, time of day, day of theweek, date, season or outside climate.

In some embodiments, the scrubber 506 can be set to run at a constantoperating mode. The capacity and efficiency of the scrubber 506 in thatmode can be selected based on the occupied space and the amount ofactivity in the occupied space, so as to maintain desirable levels ofCO₂ (and/or other substances). In some embodiments, the control system502 can control a rate of exhaust air and outside air. The baseline canbe a preset minimum. If the capacity and efficiency of the scrubber isinsufficient to handle the CO₂ load, then the rate of exhaust air andoutside air can be adjusted automatically to a higher level. The oxygenflow can be separately controlled to maintain a target level of oxygenin the occupied space. Both the control of the exhaust air valves andthe oxygen inflow can be subject to a feedback loop, with aproportional-integral-differential (“PID”) algorithm with upper andlower set points. The coupling of the oxygen concentrator to the airflow manifold can be done using any tube of duct fitting, with orwithout a control valve and/or a flow meter.

In some embodiments, the system can be designed in a modular way so thatit can be retrofitted on a pre-existing or pre-designed HVAC system.This can be beneficial in buildings that already have HVAC systems, asthe integration of the system can have relatively lower costs. Theoxygen concentrator and scrubber, with a control system, can beinstalled and connected to a conventional HVAC system without having toreplace the ductwork or the central air handling unit.

In some embodiments, the current subject matter relates to a system forcirculating air in an enclosed environment. The system can include aninlet configured to receive an outside air from outside of the enclosedenvironment and an air handling unit coupled to the inlet to receive theoutside air through the inlet and configured to receive a circulated airfrom the enclosed environment. The air handling unit can be configuredto affect a temperature of at least one of the received outside air andthe received circulated air. Based on the received outside air and thereceived circulated air, the air handling unit can be further configuredto generate air for supplying to the enclosed environment. The currentsubject matter system can also include an air circulation systemconfigured to circulate the generated air from the air handling unit tothe enclosed environment and back to the air handling unit and ascrubbing system coupled to at least one of the air handling unit andthe air circulation system and configured to reduce presence of at leastone substance in the air supplied to the enclosed environment.

In some embodiments, the current subject matter can also include one ormore of the following optional features. The scrubbing system can beconfigured to intercept at least a portion of the received circulatedair prior to the circulated air reaching the air handling unit. Thescrubbing system can intercept at least a portion of the circulated airafter the circulated air is processed by the air handling unit. In someembodiments, between approximately 1% to approximately 50% of thecirculated air can be diverted to the scrubbing system and a remainderof the circulated air can bypass the scrubbing system. In someembodiments, between approximately 3% to approximately 25% of thecirculated air can be diverted to the scrubbing system and a remainderof the circulated air can bypass the scrubbing system. In someembodiments, between approximately 5% to approximately 15% of thecirculated air can be diverted to the scrubbing system and a remainderof the circulated air can bypass the scrubbing system. In someembodiments, at least one substance in the air is carbon dioxide. Insome embodiments, at least one substance in the air can include at leastone of the following: volatile organic compounds, carbon monoxide,nitrous oxides and sulfur oxides.

The current subject matter system can include a control system coupledto at least one sensor, where at least one sensor is disposed in atleast one of the following: the enclosed environment and the aircirculation system. At least one sensor can determine a composition ofthe circulated air and provide the determination of the composition ofthe circulated air to the control system. Based on the determination ofthe composition of the circulated air, the control system can control atleast one of the following: the scrubbing system and the air inletsystem, and can be further configured to maintain a desired compositionof the circulated air. An airflow through the inlet is such that thedesired air quality can be maintained with a lower amount of outside airthan would be possible without the scrubbing system.

The scrubbing system can include at least one adsorbent, wherein aconcentration of the at least one substance is reduced by adsorption ofthe at least one substance onto the adsorbent. At least one adsorbentcan include at least one of the following: a molecular sieve, asynthetic zeolite, an activated charcoal, porous alumina, silica gel, aclay-based material, and a metal organic framework. The scrubbing systemcan include at least one additional adsorbent. At least one additionaladsorbent can be mixed with the at least one adsorbent in the scrubbingsystem. The scrubbing system can include a plurality of beds, whereineach bed in the plurality of beds is configured to intercept a flow ofcirculated air, and at least two of beds in the plurality of beds havedifferent adsorbents. The scrubbing system can also include a system forcontrolling a reversible chemical reaction that includes carbon dioxide.The reversible chemical reaction can be a sodium carbonate and sodiumbicarbonate cycle. Also, the reversible chemical reaction can be betweenan amine compound and carbon dioxide. The scrubbing system can utilizeone or more bases. The base can be an alkaline hydroxide. The scrubbingsystem can be a temperature swing adsorption system. The scrubbingsystem can further include a purge cycle during which a purge substanceis applied to the scrubbing system to release the at least one substancefrom the scrubbing system. The purge substance can be gas. The purgesubstance can be heated by applying heat generated a component of aheating, ventilation and air-conditioning system incorporating the aircirculation system.

The current subject matter system can include a heating systemconfigured to heat the purge substance. The heating system can use solarenergy. The scrubbing system can include an adsorbent and a coolingsystem configured to cool the adsorbent, wherein the cooling system usesa chilled fluid provided by the air handling unit. The scrubbing systemcan be coupled to the air circulation system such that at least one partof the circulated air is configured to flow through the scrubbing systemand at least another part of the circulated air is configured to bypassthe scrubbing system.

The current subject matter system can also include an oxygen injectionsystem that injects oxygen or an oxygen-concentrated air into thecirculated air. The current subject matter system can further include acontrol system coupled to at least one sensor disposed in the enclosedenvironment. At least one sensor can determine an oxygen level in thecirculated air and provide the determination of the oxygen level in thecirculated air to the control system. Based on the determination of theoxygen level in the circulated air, the control system can control theoxygen injection system so as to maintain a desired level of oxygen inthe circulated air. The oxygen injection system can include at least oneof the following: a pressure swing adsorption and a vacuum swingadsorption system.

FIG. 6 illustrates an exemplary process 600 for circulating air in anenclosed environment, according to some embodiments of the currentsubject matter. At 602, an outside air from outside of the enclosedenvironment and a circulated air from the enclosed environment arereceived. At 604, at least one of the received outside air and thereceived circulated air are conditioned so as to supply at least one ofthe received outside air and the received circulated air at a desiredtemperature to the enclosed environment. At 606, the conditioned air iscirculated into and from the enclosed environment. At 608, at least someof the received circulated air from the enclosed environment is scrubbedto reduce presence of at least one substance in the circulated air. At610, the scrubbed air is recirculated. At 612, at least a portion of thecirculated air is exhausted from the enclosed environment.

In some embodiments, the current subject matter relates to a controlsystem for use with an HVAC system having a gas scrubbing system forremoval of an unwanted gas from circulated air. The control system caninclude a sensor for determining an amount of the unwanted gas in thecirculated air and a controller configured to modify a rate of exhaustof circulated air or intake of outside air so as to adjust an overallair replacement according to the measured amount of unwanted gas in thecirculated air.

Further features and advantages of the invention, as well as structureand operation of various embodiments of the current subject matter, aredisclosed in detail below with references to the accompanying drawings.

Example embodiments of the methods and components of the current subjectmatter have been described herein. As noted elsewhere, these exampleembodiments have been described for illustrative purposes only, and arenot limiting. Other embodiments are possible and are covered by thecurrent subject matter. Such embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.Thus, the breadth and scope of the current subject matter should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A system for treating air of an enclosed environment comprising a scrubbing system in gaseous communication with indoor air wherein the scrubbing system is configured to reduce the concentration of at least one gaseous contaminant in the air the enclosed environment by adsorption thereof by an adsorbent contained in the scrubber. 